Right, I am doing this very subject in A Level Physics now so here goes. There are 3 possible outcomes for the universe. I will go through each possibility. 1) The open universe - This is where the universe does keep expanding forever, because the overall density is below the critical density which would cause the gravitational forces to pull everything back in again. The density of the VISIBLE matter would suggest that we are in this "open universe" state. 2) The flat universe - This is where the density of the universe is very close to the critical density, so eventually the universe will almost stop expanding and will stay roughly the same size. 3) The closed universe - Where the density is greater than the critical density, meaning that the gravitational forces in the universe would cause it to contract, eventually leading to a "Big Crunch". Current evidence suggests that this may not happen, but there is an unknown amount of "dark matter" out there, about which very little is known. But if the current estimates of this "dark matter" are correct, then there is easily substantial density to enable the universe to being to contract. But here is a key sentence from my Physics textbook: As always in physics, the solution of one problem leads to many other questions. There is always plenty to discover, and there is no end to possible questions. Because of that, I think the LHC is vital to help shed some light on what the universe is actually doing/has done. Nothing apparently. And nothing existed before the big bang, not even time itself. I told my physics teacher that this was impossible for me to get my head round. He explained it that the human mind doesn't want to venture into the theory of "nothing", so we naturally reject the possibility. It really is fascinating stuff though.